fft padding in "extractAmpPhase" function in heat simulation

hi:
We are trying to do heat simulation on a 700x1400 grid. However, we found that that dimension of heat simulation would require >190GB RAM. We therefore changed the fft padding in extractAmpPhase function to 1. We wonder what would that do to the heat simulation results? Also should the heat simulation be ran on p_max? Can it?
Thanks!